SOLVOLYSIS OF CYCLOHEXENYLIODONIUM SALT, A NEW PRECURSOR FOR THE VINYL CATION - REMARKABLE NUCLEOFUGALITY OF THE PHENYLIODONIO GROUP AND EVIDENCE FOR INTERNAL RETURN FROM AN INTIMATE ION-MOLECULE PAIR

Solvolysis of (4-tert-butyl-1-cyclohexenyl)aryliodonium tetrafluoroborates was examined in alcohol and aqueous solutions at 25-70 degrees C. Phenyliodonio group was found to be a remarkably good nucleofuge with a leaving ability about 10(6) times greater than triflate. In addition to the expected solvolysis products, 1-alkoxycyclohexene and/or cyclohexanone and iodobenzene, the internal return products, (4-tert-butyl-1-cyclohexenyl)iodobenzenes, were obtained in yields of 13-15% in methanol and aqueous solutions and of 30-40% in trifluoroethanol. The ortho derivative is the predominant isomer of these products, and this isomeric distribution is taken as indicating that the return is occurring from the intimate ion-molecule pair. The formation of a free-radical product, 4-tert-butylcyclohexene (1%), was detected during the solvolysis in the presence of 1,4-cyclohexadiene or in 2-propanol, while a considerable amount of the cationic rearrangement product, cyclopentyl methyl ketone, was obtained in the solvolysis of (2-methyl-1-cyclohexenyl)phenyliodonium tetrafluoroborate. A proposed mechanism involves mainly heterolysis to give the cyclohexenyl cation-iodobenzene pair with accompanying single electron transfer (or with competing homolysis) to lead to a free radical intermediate.